Hi Marcus, Sorry for the delay, thanks for the elaborate reply. My use case is quite specific actually, in that Im looking for a peak in a specific part of the spectrum. I had another look and failed to reproduce the problem I was having so maybe it is a problem between keyboard and chair issue but I thought it safe to clarify.
So consider this case closed for now :) Thanks again! Cheers Dirk On 12 March 2018 at 12:05, Müller, Marcus (CEL) <[email protected]> wrote: > Hi Dirk, > > On Sat, 2018-03-10 at 22:22 +0000, Dirk Gorissen wrote: > …snippety snip… >> My assumption was that the center frequency is at the middle bin >> (Shift = True) and that if I want +/- 500Hz (for example) I can just >> take the bins (middle bin index - 500) -> (middle bin index + 500) > > Think about how wide your bins are! An FFT transforms "input vector > length" =: N samples from time domain into frequency domain. Thus, > every bin represents Nyquis bandwidth / N of bandwidth. Since Nyquist > bandwidth is sampling rate, you get f_sample/N*1000 of bandwidth. > >> The python block should be trivial in that it just snips out a subset >> of the FFT bins (around the center frequency). > > Now, to act a bit like Clippy: > >> It looks like you're building a decimating low pass filter. Do you > want help with that? > > Generally, cutting out spectrum from the DFT of your signal *might* > lead to a distorted view at your signal; see [1]. > It might be OK (correct, even), however, for specific purposes. What's > the bigger thing you're planning to do? > > Best regards, > Marcus > > [1] https://dsp.stackexchange.com/questions/6220/why-is-it-a-bad-idea-t > o-filter-by-zeroing-out-fft-bins -- _________________________________________ Dr. Dirk Gorissen Mob: +44-7763-806-809 Web: dirkgorissen.com Skype: dirk.gorissen Twitter : twitter.com/dirkgor LinkedIn: linkedin.com/in/dirkgorissen _______________________________________________ Discuss-gnuradio mailing list [email protected] https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
